CA1049487A - Synthetic aircraft turbine oil - Google Patents

Abstract

SYNTHETIC AIRCRAFT TURBINE OIL
(D#73,023-F) ABSTRACT OF THE DISCLOSURE
Synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lub-ricating properties formed from the reaction of a pentaery-thritol or trimethylolpropane and an organic monocarboxylic acid containing (a) from about 0.001 to 0.05 percent of 3-amino-1H-1,2,4-triazole; (b) from about 0.3 to 5 percent of an alkyl or alkaryl phenylnaphthylamine; (c) from about 0.3 to 5 percent of a dialkyldiphenylamine; and (d) from about 0.25 to 10 percent of a hydrocarbyl phosphate ester.

Description

~9~87 BAC~GROUND OF T~ I~7ENTION
_ FIELD E~ IN~N~ION
This invention is concerned with a lubricating oil composition for a gas turbine or jet engine. Gas turbine engines are operated under extreme environmental conditions. The lubricant must be fluid at very low tem-peratures and at the same time retain its lubricating pro-perties in an engine which produces internal operating ~; temperatures of 450-550F. or above. This range of con-ditions puts such severe stresses on the lubricant that the most advanced mineral lubricating oil compositions as well as many synthetic compositions cannot be employed for lubricating turbine engines.
Currently, synthetic ester lubricating oil com- ' positions comprising an ester base from pentaerythritol or trimethylolpropane and containing a critically balanced blend of addi~ives are being employed for lubricating gas turbine engines. These ester base lubricating oils are ~ ~ .
operative o~er a wide temperature range and exhibit good ` thermal stability with a high level of oxidation and cor-rosion resistance. Mewer and more powerful gas turbine , engines designed to provide advanced Levels of supersonic -~ ~ fllght are being introduced, however, which will require resistance to substantially higher levels of thermal and oxidative stresses.
Turbine or jet engines are manufactured rom a , variety o structural metals to meet the problems o high - temperatures, high speed turbine operation, and bearing stresses and it is conventional to employ a metal deacti-; ~ .
~ator in the synthetic ester base lubricating oil composi-" ~

, ~ :

~4~41~7 tion to minimize metal corrosion in this environm~t. The metal deactivator is postulated to form a monomolecular protective layer bonded to the exposed surfaces of the metals most subject to corrosion.
A wide range of materials have heretofore been proposed as metal deactivators for use in synthetic ester base lubricating oil compositions. Condensation products of salicylaldehyde and hydrazine derivatives and fatty acid salts of the condensation products have been proposed with the salts of l-salicylalaminoguanidine and C14 to C18 aliphatic carboxylic acids being preferred in this clas-sification.
Salicylaldehyde semicarbozone and its Cl to C20 alkyl derivatlves as exemplified by methyl and isopropyl salicylaldehyde semicarbazone represent another class of metal deactivators.
Certain members of the hydroxyanthraquinones exemplified by 1,4 dihydroxyanthraquinone (quinizarin), are effective metal deactivators while other related anth-raquinones are considered to be ineffective.
Another group of metal deactivators includes the Cl to C20alkyl gallates, preferably propyl gallate, neopentyl glycol disebacate, sebacic acid, azelaic acid and adipic acid.
Still another class of metal anti-corrosion agents are the pyridylamines including dipyridylamines such as

2,2'-dipyridylamine.
The triazoles are also effective metal deactivators - .
~;

~ .

9i4~7 and this class includes 1,2,3-benztriazole, methyl-1,2,3-benztriazole, 3-amino-5-methyl-1,~,4-triazole, 3~-amino-5-phenyl-1,2,4-triazole, 3-amino-5-pyridyl--1,2,4-triazole and 5,5'-diamino-3,3-bi (1,2l4-triazole).
The conditions under which an ester base lubricant must perform are so demanding that the selection of the metal deactivator becomes critical in the formulation of a clean deposit-resistant lubricant. Even though the known metal deactivators are effective for the designated purpose, they frequently cause or contribute to other serious problems arising from the use of the lubricant.
For example, metal deactivators are commonly responsible for substantially increasing engine deposits as determined in the Alcor Deposition Test. They also can cause unac-ceptable staining and pitting or erosion of the magnesium metal present in the engine and engine accessory units, such ; as the constant speed drive units which generate electrical power.
DESCRIPTION OF THE PRIOR ART ~::
.
U.S. 3,344,068 discloses synthetic ester base lub-rication oil composition containing many metal deactivators including substituted ~mlnQ- and benz~ triazoles.
U.S. 3,427,111 discloses a synthetic lubricating ~ oil composition employing a pentaerythritol ester base con-`l taining 1) arylamine type anti-oxidants, such as dipheny-lamine and phenyl-alpha napththylamine, 2) a copper surface passivator, namely a salt of l-salicylalaminoguanidine and a C14 ~ 18 aliphatic car~oxylic acidr 3) a metal deactivator, namely a polyhydroxyanthraquinone and 4) an organic phos-;i 30 phorus ester in the form of a phosphate or a phosphite.
British Patent No. 1,180,387 discloses a synthetic lubricating oil composition containing a copper passivator of the azole type, salicylaldehyde and hydraæine.

-~948~
_UMMARY OF THE INVENTION
The syn-thetic lubrica-ting oil composition oE -the inven-tion comprises a major portion of an alipha-tic ester base oil having lubrica-ting proper-ties containing 3-amino-1-H-1,2,~--triazole, an al]cylphenyl or alkarylphenyl naph-thyl-amine, a dialkyldiphe:nylamine, and a hydrocarbyl phospha-te.
More specifically, -the lubrica-ting oil composition of -the invention comprises a major portion of an aliphatic ester base oil formed from the reac-tion of a pentaerythritol or -trimethylolpropane and an organic monocarboxylic acid having from about 2 to 18 carbon atoms per molecule con- :
taining:
a) from about 0.001 -to 0.05 weigh-t percent of 3-amino-lH-1,2,4--triazole, b) from about 0.3 -to 5 percen-t by weigh-t oE the lubrica-ting oil composition of alkyl or alkaryl deriva-tives of phenyl ~ or ~ naph-thylamines in which the alkyl radicals have from 3 -to 12 carbon atoms, c) from about 0.3 to 5 percent of a dialkyl-diphenylamine in which the alkyl radicals have from 4 to 12 carbon atoms, and d) from abou-t 0.25 to 10 percen-t of a hydrocarbyl phosphate in which said hydrocarbyl radical con-tains an aryl ring and has from about 6 to 18 carbon atoms.
The novel lubricating oil of the invention provides outstanding thermal and oxidative stability, reduces me-tal deposits and effe~ively prevents magnesium metal stain-ing, pitting, and corrosion. These valuable proper-ties :`, : .

~L0~9~37 were obtained from a critically formulated synthetic ester base lubricating oil blend. The results of the novel com-position were surprising and unexpected in equaling or surpassing outstanding commercial synthetic ester base lubricating oil compositions in oxidatîon stability and deposits control while additionally providing unique pro-tection against magnesium pitting and staining.
The base fluid component of the lubricant of the invention is an ester-base fluid prepared from pentaery-thritol or trimethylolpropane and a mixture of hydrocarbyl monocarboxylic acids. Polypentaerythritols, such as di-pentaerythritol, tripentaerythritol and tetra-pentraey-thritol can also be employed in the reaction to prepare the base oil.
The hydrocarbon monocarboxylic acids which are used to form the ester-base fluid include the straight-chain and branched-chain aliphatic acids, cycloaliphatic acids and aromatic acids as ~7ell as mixtures of these acids.

The acids employed ha~e from about 2 to 18 carbon atoms per molecule, and preferably from about 5 to lO carbon atoms. Examples of suitable specific acids are acetic, propionic, butyric, valeric, isovaleric, caproic, decanoic, cyclohexanoic, naphthenic, benzoic acid, phenylacetic, tertiary-butylacetic acid ar~ 2-ethylhexanoic acid.
; In general, the acids are reacted in proportions leading to a completely esterified pentaerythritol or trimethylolpropane with the preferred ester bases being the pentaerythritol tetraesters. E~:am~les of such commer-cially a~ailable tetraesters incLude pentaerythritol tetracaproate, which is prepared from purified pentaery-thrit.ol and crude caproic acid containing other C5-lO
monobasic acids. Another suitable tetraester is prepared ~5~

~ ' ' : . . ' ' . , ~ ' ' ' ~a~4~487 from a technical grade pentaerythritol and a mixture of acids comprising 38 percent valeric, 13 percent 2-methyl pentanoic, 32 percent octanoic and 17 percent pelargonic acids. Another effective ester is the triester af tri-methylolpropane in which the trimethylolpropane is ester-ified with a monobasic acid mixture consisting of 2 per-cent valeric, 9 percent caproic, 13 percent heptanoic, 7 percent octanoic, 3 percent caprylic, 65 percent pelargonic and 1 percent capric acids. Trimethylolpropane triheptan-oate is also a suitable ester base.
The ester base comprises the major portion of the fully formulated synthetic ester base lubricating oil com- ' position. In general, this ester base fluid is present in concentrations from about 90 to 98 percent of the com-position.
The essential 3-aminotriazole component of the lubricating oil composition of the invention is repre-sented by the formula:

HC N

N' ,, The essential alkyl or alkary; phenyl naphthy-lamine component of the invention is represented by the formula:
,, H

R ~ , ~

in which R is an alkyl or alkaryl radical having from about 3 to 12 carbon atoms. This radical can be a straight or branched chain, alkyl radical with the tertiary alkyl ~, structure being preferred or it can be an alkylaryl radical.
' :

1C~4~37 The napthylamine can be either an alpha or beta naphthy-lamine. Specific effecti~e compounds of this class in-clude N-(~-t-octylphenyl)- -naphthylamine, N-(4-cumyl~
phenyl)-6-cumyl-B-naphthylamine, N-(p-t-octylpheny)-naphthylamine and the corresponding _-t-dodecylphenyl, p-t-butylphenyl, and p-dodecylphenyl- and - - naphthyl-amines. The preferred naphthylamines arle those in which R is a ter~iary alkyl radical having from 6 to 10 carbon atoms. The preferred concentration of this component is ; 10 from about 0.5 to 2.5 percent.
Another essential component of the lubricating oil composition of the invention is a dialkyldiphenylamine.
These compounds are represented by the formula:
R ~ ~ R

in the R is an alkyl radical having from about 4 to 12 carbon atoms. Suitable alkylamines include dioctyldipheny~
lamine and similar compounds. The preferred class of di-alkyl diphenylamines are those in which R is an alkyl rad-ical having from 8 to 10 carbon atoms. Dioctyldiphenyl-amine is the preferred compound and the preferred concen-tration is from 0.5 to 2.0 percent.
The final essential component of the lubricating oil composition of the invention is a hydrocarbylphosphate ester, more specifically a trihydrocarbyl phosphate having the formul (RO) 3PO in which R is a hydrocarbyl radical i.e.
an alkyl, aryl, alkaryl, cycloalkyl or aralkyl radical or mixture thereof having from 2 to 12 carbon atoms and pre-ferably from 4 to g carbon atoms. Effective specific com-pounds include tricresylphosphate, cresyl diphenylphosphate triphenylphosphate, tributylphosphate, tri(2-ethylhexyl)-phosphate and tricyclohexyl phosphate. These compounds are ~-' ' - . : . .. . .

preferably present in the l~ricating oil compositi~n in a concentration ranging from abou~ 0.5 to 5 percent.
The lubricating oil composition of the in~ention was tested for its oxidation and corrosion resistance in the 425F/48 Hr Oxidation and Corrosion Test which was conducted in accordance with Standard No. 791a (issued December 31, 1961) except for modifications to conform to Pratt and Whitney 521B Specifications. The bath temperature is maintained at 425F. + 1F. instead of at 250F. and the test is conducted for a period of 48 hours instead of 168 hours as specified in the original test.
The ester base oils employed in preparing the lub-ricating oil compositions tested below comprised pentaery-thritol containing a minor amount of dipentaerythritol estified with mixtures ~f fatty acids.
Base Oil A consisted of technical grade pentaery-; thritol ester made from a mixture of carboxylic acid con-sisting of (mole %):
i - C5 8 + 3~
n - C5 23 -~ 5 n - C6 20 -~ 5 n - C7 27 + 5 .
n C8 n - Cg 16 + 3 ; This ester base oil had the following properties:
Viscosity, cs at 210F 5.01 ~i Viscosity, cs at 100F. 25.6 Viscosity, cs at -40F. 7005 Viscosity Index 140 Flash, F. 515 Base Oil B was similar to Base Oil A
but consisted of pentaerythritol ester made from the fol-9~
lowing mixture of carboxylic acids (mole %):
i - C5 1~ + 3 n - C5 28 + 5 n - C6 11 + 5 n - C7 17 + 5 n - C~ 20 + 5 n - Cg 12 ~ 5 n - C10 1 Max.
Table I below lists the compositions of the ester base lubrican~s which were prepared and tested and ~able II gives the results of Table I.

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o o U~
, . .. . ....

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el' o o . . . -. - .
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,1 tn I ,1 ~ ,1 1 0 :' cn :, ~ a / o\ ~ ,N~
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a~ v,1 ~ a ~: o . ~ o P~ ~ a) ~ ~ a) ~I
~ 1~ ~ ~ ~ ~ ~ d I O
o ~ m ~ ~ 1 ~ N
~1 E~ a) 1 1 ,~ ~ O ~ ~ I I rl S-l ~rl rl ~ ~1 O h Ul o o a~ ~ N
o rd ~ rl O ~rl t~. a) O ~ 1 E3 N ~:
~ U~ (1) ~1 ~rl ~ rl o ~ I I I a m R~ 7 m ~

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E~ ~ o o O
~ S:~ H 11~o. ~ ~D1`~ D C~ .
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r~

3 ~ ~ g a~ n . ~ ~ O O o O O ~ ~1 ~ ~ O O O O Or~ 1 ,, .tJ

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~ rl rl rl t ~rlrl~ rl ~ ~
O U~ ~ ,.
~ 401 ', ' ~ C~ O ~ O ~ V C~ ~ .

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Runs 1 through 5 in Table II are representative of ester base lubricant compositions of this invention. These lubricants pass all of the required specifications in the 425F./48 Hour Oxidation-Corrosion Test.
Runs 6 and 7 employed similar compositions except that the lubricant contained no aminotriazole metal de-activator. These lubricants caused excessive copper metal corrosion and failed this test.
The lubricant of the invention was tested in the Erdco Bearing Test, Type 1.5, in comparison to other ester base lubricants. This test is designed to determine the cleanliness of the lubricant in service by measuring the deposits formed. The oil consumption is also im-portant as prescribed in U.S. Navy MIL-L-23699B specifica-tion. The results of this 100-hour test are set forth in the following Table.

~' ., ', .

.
:- .. . .. . .

9~37 to d .' X ~ .
~ fd ~ r- ~ co o In ~ 10 o-- CO ~ ~ o ~o U~
O O ~D 1`0 O
~: ~ ~ , -' ,, ~ .
O ~
~ .
.
~ . ~ .
~ .
.,, .,, ,, u~ n ~ ~ ~ X
~q o a~ ~ ~D 1~In td o o o o ~ U . .
~, . ,"
H ~ t~ o oo o o ~Xd ~ I .. .
m u ~ g~ ~I
~ ~ ~ H ~i ,1 o ,1 o ~

U~ . ~ , . . .
,i H ~, ~ o u~ o o al O ~ n o ~ o a~ ~ oo ~dl u~ ~ U
. ' ~i 0 ~ ~ I
`_ 11 ~ ~ ~ ~ ~ ~ co ~ ~
o.
O O
L~ ~
~ ~ ~ ~
.~ ~ rl rl ,~ ~
~ ~ I ~
~ ~ m o r~ o o ~ ~ ~ rl rl U~
;l ~ . ~ .~ ~, ~, ~ C) o ~ ~ ~ .~ ' ,.
.

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.. . . . . ~ ; ~ . , ~ , . .
: ... ,, . .. ,. . .. - , . .

~al 4~4~7 From the foregoi~g table, it can be seen that the lubricants in Runs 1 and 2 of this invention were superior to Runs 3 and 5 in Deposits Demerit rating by 40% and 60% respe-ctively and superior to Runs 3,4 and 5 irL oil consumption.
Runs l and 2 gave remarkably low Filter Oeposits, Runs 3 and

4 both producing about 140~ more filter deposits. Run 5, using commercial Fluid C, produced about 30~ more ilter de-posits than Run l and an oil consumption level of 2025 ml.

which exceeds the U.S. Navy Specification of a maximum of 2000 ml.

The lubricant of the invention was also tested in the Alcor High Temperature Deposition Test. This test is included in the (proposed) U.S. Navy XAS-2354 Specification.
Deposits are determined as Tube Deposits from the tower tube and as Filter Deposits. The maximum allowable tube deposit is 15.0 mg. The tower tube temperature was main-tained at 550F. The results of this test are set forth below:

~)49487 , _.
~a ~a .,, o O
o ~ ~ ~ ~, a u~ u, ~ ~ .
~ ~ ~.
r~ .
s~
r-l ~

O 0~ 0 i~ ~ O
~q O ~ ~ ~ ~ C~
~ a~ ~1 ~J ~ .

~ 1~ LO
~! 1 ~ ~ ~ 'I r~l ~i ~
~Q) a ~
co u~ a O O O
O ,~ ,i rl l¢ P~ O h ~ O O O r~l ~I r-l r-l U U 14 .
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.,,,, . ~

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.. . . .. . . .
' ' ' ~ .' ~ ' ' , , ~ ' . ' ' . ', '. , , ' " ,:

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Runs 1 and 2 in the above Tab:Le represent the pre sent invention and the lubricant compositions.employed gave Tube Deposits of 3.7 and.2.8 milligrams respectively and E~ilter Deposits of 25~4 and 39 milliqrams. respectively.
Run 3 employed a lubricant containing benzotriazole as the metal deactivator and gave Tube Deposits of 11.1 milligrams Commercial Fluid C excceded the specification limit for Tube Deposits and all of the. commercial fluids gave E~ilter Deposits that were significantly greater than the deposits caused by the lubricants of this.invention. This test dem- :
onstrates superior performance in.impro~ed deposits control due to the lubricant of the invention.
The foregoing tests demonstrate the superior clean-liness in engine deposits of the lubricants of the invention in comparison to a variety of known synthetic lubricating oil compositions including some highly successful.commer-cial lubricants.

.

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. .

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A synthetic lubricating oil composition com-prising a major portion of an aliphatic ester base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and a saturated hydrocarbyl monocarboxylic acid having from about 2 to 18 carbon atoms per molecule, consisting of a) from about 0.001 to 0.05 weight percent of 3-amino-1H-1,2,4-triazole, b) from about 0.3 to 5 percent by weight of the lubricating oil composition of an alkyl or alkaryl phenyl naphthylamine in which the alkyl radical has from 3 to 12 carbon atoms, c) from about 0.3 to 5 percent of a dialkyl-diphenylamine in which the alkyl radicals have from 4 to 12 carbon atoms, and d) from about 0.25 to 10 percent of a trihydro-carbyl phosphate in which said hydrocarbyl radical contains an aryl ring and contains from about 2 to 12 carbon atoms.

2. A lubricating oil composition according to Claim 1 containing from about 0.002 to 0.02 weight percent of said 3-amino-1H-1,2,4-triazole.

3. A lubricating oil composition according to Claim 1 containing from about 0.003 to 0.008 weight per-cent of said 3-amino-1H-1,2,4-triazole.

4. A lubricating oil composition according to Claim 1 containing from about 0.5 to 2.5 percent of an octylphenyl- ? -or .beta. naphthylamine, from about 0.5 to 2.0 percent of a dioctylphenylamine, and from about 0.5 to

5 percent of a trihydrocarbyl phosphate.